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<p>逻辑运算符应用标准布尔代数运算到其运算数。
</p>
<table class="wikitable" style="font-size:85%;">

<tr style="text-align:center">
<th> 运算符
</th>
<th> 运算符名
</th>
<th> 示例
</th>
<th> 结果
</th></tr>
<tr style="text-align:center">
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span></span></span>
</td>
<td> 逻辑非
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>a</span></span>
</td>
<td> <b>a</b> 的逻辑否定
</td></tr>
<tr style="text-align:center">
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">&amp;&amp;</span></span></span>
</td>
<td> 逻辑与
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c">a <span class="sy3">&amp;&amp;</span> b</span></span>
</td>
<td> <b>a</b> 与 <b>b</b> 的逻辑与
</td></tr>
<tr style="text-align:center">
<td> <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">||</span></span></span>
</td>
<td> 逻辑或
</td>
<td> <span class="t-c"><span class="mw-geshi c source-c">a <span class="sy3">||</span> b</span></span>
</td>
<td> <b>a</b> 与 <b>b</b> 的逻辑或
</td></tr></table>
<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E9.9D.9E">逻辑非</span></h3>
<p>逻辑非运算符拥有形式
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <code><b>!</b></code> <span class="t-spar">expression</span>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中
</p>
<table class="t-par-begin">


<tr class="t-par">
<td> <span class="t-spar">expression</span>
</td>
<td> -
</td>
<td> 拥有任何<a href="type.html#.E7.B1.BB.E5.9E.8B.E7.BB.84.E5.88.AB" title="c/language/type" class="mw-redirect">标量类型</a>的表达式
</td></tr></table>
<p>逻辑非运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型。若 <span class="t-spar">expression</span> 求值为不等于零的整数则其值为 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 。若 <span class="t-spar">expression</span> 求值为等于零的整数则其值为 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。（故 <span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>E</span></span> 与 {{c|(0==E)} 相同）
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdbool.h&gt;</span>
<span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;ctype.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    bool b <span class="sy1">=</span> <span class="sy3">!</span><span class="br0">(</span><span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">4</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 非 true</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"!(2+2==4) = %s<span class="es1">\n</span>"</span>, b <span class="sy4">?</span> <span class="st0">"true"</span> <span class="sy4">:</span> <span class="st0">"false"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="kw4">int</span> n <span class="sy1">=</span> <a href="../string/byte/isspace.html"><span class="kw534">isspace</span></a><span class="br0">(</span><span class="st0">'a'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 若 'a' 空格则为零，否则为非零</span>
    <span class="kw4">int</span> x <span class="sy1">=</span> <span class="sy3">!!</span>n<span class="sy4">;</span> <span class="co1">// "bang-bang" ，常用的 C 手法，映射标量为 [0,1]</span>
                 <span class="co1">// （所有非零值变为 1 ）</span>
    <span class="kw4">char</span> <span class="sy2">*</span>a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="st0">"nonspace"</span>, <span class="st0">"space"</span><span class="br0">}</span><span class="sy4">;</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%s<span class="es1">\n</span>"</span>, a<span class="br0">[</span>x<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 现在能安全地以 x 为 2 个 int 的数组的下标</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">!(2+2==4) = false
nonspace</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E4.B8.8E">逻辑与</span></h3>
<p>逻辑与表达式拥有形式
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">lhs</span> <code><b>&amp;&amp;</b></code> <span class="t-spar">rhs</span>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中
</p>
<table class="t-par-begin">


<tr class="t-par">
<td> <span class="t-spar">lhs</span>
</td>
<td> -
</td>
<td> 拥有任何标量类型的表达式
</td></tr>
<tr class="t-par">
<td> <span class="t-spar">rhs</span>
</td>
<td> -
</td>
<td> 拥有任何标量类型的表达式，仅若 <span class="t-spar">lhs</span> 比较不等于 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 才求值
</td></tr></table>
<p>逻辑与运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型，而若 <span class="t-spar">lhs</span> 与 <span class="t-spar">rhs</span> 都比较不等于零则拥有值 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。否则拥有值 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> （若 <span class="t-spar">lhs</span> 或 <span class="t-spar">rhs</span> 之一或两者比较等于零）。
</p><p>在 <span class="t-spar">lhs</span> 的求值后有<a href="eval_order.html" title="c/language/eval order">序列点</a>。若 <span class="t-spar">lhs</span> 的结果比较等于零，则完全不求值 <span class="t-spar">rhs</span> （是谓<i>短路求值</i>）。
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdbool.h&gt;</span>
<span class="co2">#include &lt;stdio.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    bool b <span class="sy1">=</span> <span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span><span class="sy1">==</span><span class="nu0">4</span> <span class="sy3">&amp;&amp;</span> <span class="nu0">2</span><span class="sy2">*</span><span class="nu0">2</span><span class="sy1">==</span><span class="nu0">4</span><span class="sy4">;</span> <span class="co1">// b == true</span>
 
    <span class="nu0">1</span> <span class="sy1">&gt;</span> <span class="nu0">2</span> <span class="sy3">&amp;&amp;</span> <a href="../io/puts.html"><span class="kw836">puts</span></a><span class="br0">(</span><span class="st0">"this won't print"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="kw4">char</span> <span class="sy2">*</span>p <span class="sy1">=</span> <span class="st0">"abc"</span><span class="sy4">;</span>
    <span class="kw1">if</span><span class="br0">(</span>p <span class="sy3">&amp;&amp;</span> <span class="sy2">*</span>p<span class="br0">)</span> <span class="co1">// 常用的 C 手法：若 p 非空 *与* 若 p 不指向字符串尾</span>
    <span class="br0">{</span>           <span class="co1">// （注意拜短路求值所赐，这不会试图解引用空指针）</span>
    <span class="co1">// ...      // ……然后做一些字符串处理</span>
    <span class="br0">}</span>
<span class="br0">}</span></pre></div></div>
<p><br> 
</p>
</div>
<h3><span class="mw-headline" id=".E9.80.BB.E8.BE.91.E6.88.96">逻辑或</span></h3>
<p>逻辑或表达式拥有形式
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td class="t-sdsc-nopad"> <span class="t-spar">lhs</span> <code><b>||</b></code> <span class="t-spar">rhs</span>
</td>
<td class="t-sdsc-nopad">
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>其中
</p>
<table class="t-par-begin">


<tr class="t-par">
<td> <span class="t-spar">lhs</span>
</td>
<td> -
</td>
<td> 拥有任何标量类型的表达式
</td></tr>
<tr class="t-par">
<td> <span class="t-spar">rhs</span>
</td>
<td> -
</td>
<td> 拥有任何标量类型的表达式，仅若 <span class="t-spar">lhs</span> 比较等于 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> 才求值
</td></tr></table>
<p>逻辑或运算符拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">int</span></span></span> 类型，而若 <span class="t-spar">lhs</span> 或 <span class="t-spar">rhs</span> 比较不等于零则拥有值 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu0">1</span></span></span> 。否则它拥有值 <span class="t-c"><span class="mw-geshi c source-c">​<span class="nu0">0</span>​</span></span> （若 <span class="t-spar">lhs</span> 与 <span class="t-spar">rhs</span> 都比较等于零）、
</p><p>在 <span class="t-spar">lhs</span> 的求值后有<a href="eval_order.html" title="c/language/eval order">序列点</a>。若 <span class="t-spar">lhs</span> 的结果比较不等于零，则完全不求值 <span class="t-spar">rhs</span> （是谓<i>短路求值</i>）。
</p>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdbool.h&gt;</span>
<span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;string.h&gt;</span>
<span class="co2">#include &lt;errno.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    bool b <span class="sy1">=</span> <span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">4</span> <span class="sy3">||</span> <span class="nu0">2</span><span class="sy2">+</span><span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">5</span><span class="sy4">;</span> <span class="co1">// true</span>
    <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"true or false = %s<span class="es1">\n</span>"</span>, b <span class="sy4">?</span> <span class="st0">"true"</span> <span class="sy4">:</span> <span class="st0">"false"</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="co1">// 逻辑或能像 perl 的 "or die" 一样使用，只要 rhs 拥有标量类型</span>
    <a href="../io/fopen.html"><span class="kw819">fopen</span></a><span class="br0">(</span><span class="st0">"test.txt"</span>, <span class="st0">"r"</span><span class="br0">)</span> <span class="sy3">||</span> <a href="../io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"could not open test.txt: %s<span class="es1">\n</span>"</span>, <a href="../string/byte/strerror.html"><span class="kw574">strerror</span></a><span class="br0">(</span><span class="kw2">errno</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>可能的输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">true or false = true
could not open test.txt: No such file or directory</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.5.3.3 Unary arithmetic operators (p: 89)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 6.5.13 Logical AND operator (p: 99)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 6.5.14 Logical OR operator (p: 99)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.5.3.3 Unary arithmetic operators (p: 79)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 6.5.13 Logical AND operator (p: 89)
</li></ul>
</dd></dl>
<dl><dd><ul><li> 6.5.14 Logical OR operator (p: 89)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 3.3.3.3 Unary arithmetic operators 
</li></ul>
</dd></dl>
<dl><dd><ul><li> 3.3.13 Logical AND operator 
</li></ul>
</dd></dl>
<dl><dd><ul><li> 3.3.14 Logical OR operator 
</li></ul>
</dd></dl>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<p><a href="operator_precedence.html" title="c/language/operator precedence">运算符优先级</a>
</p>
<table class="wikitable">

<tr style="text-align:center">
<th colspan="7"> 常用运算符
</th></tr>
<tr style="text-align:center">
<td> <a href="operator_assignment.html" title="c/language/operator assignment">赋值</a>
</td>
<td> <a href="operator_incdec.html" title="c/language/operator incdec">自增<br>自减</a>
</td>
<td> <a href="operator_arithmetic.html" title="c/language/operator arithmetic">算术</a>
</td>
<td> <strong class="selflink">逻辑</strong>
</td>
<td> <a href="operator_comparison.html" title="c/language/operator comparison">比较</a>
</td>
<td> <a href="operator_member_access.html" title="c/language/operator member access">成员<br>访问</a>
</td>
<td> <a href="operator_other.html" title="c/language/operator other">其他</a>
</td></tr>
<tr style="text-align:center">
<td>
<p><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy1">=</span> b<br>
a <span class="sy2">+</span><span class="sy1">=</span> b<br>
a <span class="sy2">-</span><span class="sy1">=</span> b<br>
a <span class="sy2">*</span><span class="sy1">=</span> b<br>
a <span class="sy2">/</span><span class="sy1">=</span> b<br>
a <span class="sy2">%</span><span class="sy1">=</span> b<br>
a <span class="sy3">&amp;</span><span class="sy1">=</span> b<br>
a <span class="sy3">|</span><span class="sy1">=</span> b<br>
a <span class="sy3">^</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;&lt;=</span> b<br>
a <span class="sy1">&gt;&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">++</span>a<br>
<span class="sy2">--</span>a<br>
a<span class="sy2">++</span><br>
a<span class="sy2">--</span></span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy2">+</span>a<br>
<span class="sy2">-</span>a<br>
a <span class="sy2">+</span> b<br>
a <span class="sy2">-</span> b<br>
a <span class="sy2">*</span> b<br>
a <span class="sy2">/</span> b<br>
a <span class="sy2">%</span> b<br>
~a<br>
a <span class="sy3">&amp;</span> b<br>
a <span class="sy3">|</span> b<br>
a <span class="sy3">^</span> b<br>
a <span class="sy1">&lt;&lt;</span> b<br>
a <span class="sy1">&gt;&gt;</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c"><span class="sy3">!</span>a<br>
a <span class="sy3">&amp;&amp;</span> b<br>
a <span class="sy3">||</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c">a <span class="sy1">==</span> b<br>
a <span class="sy3">!</span><span class="sy1">=</span> b<br>
a <span class="sy1">&lt;</span> b<br>
a <span class="sy1">&gt;</span> b<br>
a <span class="sy1">&lt;=</span> b<br>
a <span class="sy1">&gt;=</span> b</span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c">a<span class="br0">[</span>b<span class="br0">]</span><br>
<span class="sy2">*</span>a<br>
<span class="sy3">&amp;</span>a<br>
a<span class="sy2">-</span><span class="sy1">&gt;</span>b<br>
a.<span class="me1">b</span></span></span>
</p>
</td>
<td>
<p><span class="t-c"><span class="mw-geshi c source-c">a<span class="br0">(</span>...<span class="br0">)</span><br>
a, b<br>
<span class="br0">(</span>type<span class="br0">)</span> a<br>
<span class="sy4">?</span> <span class="sy4">:</span><br>
<span class="kw4">sizeof</span><br>
_Alignof</span></span> <span class="t-mark-rev t-since-c11">(C11 起)</span>
</p>
</td></tr>
</table>
<table class="t-dsc-begin">

</table></div>
</div>

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